You will need to start by scanning for codes. There are electronics with the transmission but unless you work on transmissions you'll need to have it diagnosed at a shop.
Use this link to find a good shop near you.
https://repairpal.com/repair-shops
Alex
RepairPal Certified shops can diagnose and repair your 2006 Ford Expedition. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.